JP4416529B2 - Method for inspecting the presence of cracks in the finger dovetails of wheels and buckets - Google Patents

Description

  The present invention relates to a method for inspecting a wheel and bucket finger dovetail for the presence of cracks in the material surrounding the pinhole in which the pins are received to secure the wheel and bucket to each other, and more particularly to the presence or absence of finger cracks. It relates to the use of a phased array ultrasonic probe for inspecting finger dovetails in the field.

  In turbines, such as steam turbines, the edge of the wheel is often provided with a plurality of axially projecting fingers spaced apart from one another in the axial direction defining the dovetail, and the wheel dovetail is secured to the wheel. Receiving substantially complementary individual finger dovetails in the bucket. The bucket dovetail and the wheel dovetail mesh with each other, and along the edge of the wheel, there are at least two, usually three pinholes that penetrate the bucket finger and the wheel fingers, aligned axially, each of which is a pinhole. The bucket position is located along the radius. To keep the bucket secured to the wheel, pins are inserted axially into the aligned pinholes. It will be appreciated that the pin applies a radial load of the bucket to the wheel. As service life increases, over time, this radial load causes stress-related cracks in the entire area of one or more wheel fingers, particularly at pinhole locations in the wheel fingers. Stress-related cracks tend to have a generally tangential orientation and usually spread circumferentially from the pinhole. In some cases, a crack may connect to an adjacent pinhole. If a crack is formed in one or both of the wheel finger dovetail and bucket finger dovetail, the wheel dovetail or bucket dovetail may be damaged, the bucket speed may be impaired, and the turbine and / or power generation section may be damaged. It will be appreciated that occurs.

The danger of this turbine failure has been recognized in the industry. Therefore, periodic inspection of the wheel finger dovetail and the bucket finger dovetail is instructed. Needless to say, periodic inspections can be performed by removing the bucket from the wheel. However, removing each bucket from the wheel after using the turbine is labor intensive, time consuming, and therefore expensive, even if several buckets are removed as samples. is there. Furthermore, it is often very difficult to remove the pins that secure the bucket to the wheel turbine in order to release the bucket from the wheel. Typically, the pins are hammered out or a gun loaded with explosives is used to eject the pins that are particularly difficult to remove. Moreover, in order to remove a pin, the method of using a drill and the EDM process are also employ | adopted. After removing the pin and bucket from the wheel, the finger dovetail can be inspected, for example, using magnetic particle testing techniques. After the test, the bucket and pin must be re-installed on the wheel.
U.S. Pat.No. 3952581 U.S. Pat.No. 3960006 U.S. Pat.No. 4229796 U.S. Patent No. 4577507 U.S. Pat.No. 4,757,716 US Patent No. 5623107 US Patent No. 6019001 U.S. Patent No. 6065344

  However, some of the pins may be damaged when removing the pins and must be replaced. In the magnetic particle inspection, it is necessary to prepare the surface before the inspection. Furthermore, significantly logistic support means in the form of cranes, laydown areas, etc. are required to complete pin removal, inspection and pin re-insertion to secure the bucket to the wheel. Accordingly, there is a need to in-situ inspect the turbine wheel finger dovetail and bucket finger dovetail in situ.

  Thus, in a preferred embodiment of the present invention, the bucket is not removed from the wheel, only a minimal number of pins are removed and the material adjacent to the wheel and bucket finger dovetail pinholes is checked for cracking. A method for in-situ inspection is provided. That is, the pins are preferably spaced regularly along the wheel, for example, every other bucket, and only one of the three pins that secure the bucket to the wheel, preferably the middle pin. Only removed from the pinhole. Once a selected pin is removed, an ultrasonic probe, or phased, with one or more individual elements to detect crack information in both circumferentially adjacent pinholes and radially adjacent pinholes An array ultrasonic probe is inserted into the pinhole. In the case of an ultrasonic probe having one or more elements, the probe is mechanically rotated about its axis in the aligned pinhole so that the material around the aligned pinhole is completely circumferential Scanned. Thereafter, the ultrasonic information is analyzed for crack detection.

  In the case of a phased array ultrasonic probe, the probe can be scanned electronically in the circumferential direction without mechanical movement of the probe, i.e. without rotating the probe about the pinhole axis. The size is determined to be inserted into the pinhole. Also, the ultrasonic beam can be focused at different distances. It is possible to encode the position of the probe and combine it with ultrasound information to accurately image inspection data for analysis. Rotate the electron beam in the circumferential direction by mechanically moving the ultrasonic probe in the axial direction and pulsing the individual phased array elements, eg, piezoelectric elements, along the probe's perimeter with appropriate delay In combination, the material around the pinhole can be completely scanned. By synchronizing the axial scan with the ultrasonic pulse motion, a continuous spiral scan path can be generated. Alternatively, multiple scans / indexes to perform circumferential scans at one axial distance, and then gradually and repeatedly advance the probe in the axial direction to inspect material adjacent to the axial length of the pinhole It is also possible to create steps. In this way, it will be appreciated that the ultrasonic beam detects the formation of a crack opening into a hole adjacent to the pinhole receiving the probe. Crack formation in the pinhole receiving the probe can be confirmed by another test technique such as an eddy current test after the probe has been withdrawn. As a result, a minimal number of pins can be removed from the pinhole and the in-situ inspection process can be performed without removing the bucket from the wheel, while the crack detection in the wheel and bucket finger dovetails High sensitivity is obtained without change.

  As yet another technique, the method of the present invention involves sampling finger dovetails spaced along the wheel, which is insufficient to detect all cracks. That is, the ultrasonic sampling probe is used only in pinholes that are spaced apart widely, and therefore does not exist in a predetermined position for detecting all cracks. In this way, it is possible to determine the statistical probability of crack formation, for example, the absence of cracks, the probability of cracks being very low, or high. When the probe detects a crack present in the dovetail material, the crack can be further investigated, for example, by removing the bucket and performing other tests to determine the extent of the crack. It is also possible to shorten the inspection interval along the wheel to ensure detection of all cracks rather than just sampling.

  In a preferred embodiment according to the present invention, to pin the wheel and bucket together, when the wheel has a plurality of aligned holes through the finger dovetail, the finger dovetail of at least one of the wheel and bucket is A method for inspecting the process of inserting an ultrasonic probe into one of the aligned holes in at least one of the wheel and bucket and identifying cracks present in the material surrounding the hole A method comprising rotating an ultrasound probe about its axis within an aligned hole so as to electronically scan the material surrounding the hole.

  In another preferred embodiment according to the present invention, when the wheel has a plurality of aligned holes through the finger dovetail to pin the wheel and bucket together, the finger of at least one of the wheel and bucket is used. A method for inspecting a dovetail, the step of inserting a phased array ultrasonic probe into one of the aligned holes in at least one of the wheel and bucket, and a crack present in the material surrounding the hole To actuate the ultrasonic probe to electronically scan the material of the finger dovetail of one of the wheel and bucket around the hole.

  In yet another preferred embodiment according to the present invention, there is a method for in-situ inspecting a wheel dovetail and bucket dovetail for the presence of cracks in the material around the pinhole containing a plurality of pins that secure the bucket and wheel together. (A) removing a pin from the pinhole that secures one of the buckets to the wheel; (b) inserting a phased array ultrasonic probe into the pinhole; and (c) phased array ultrasound. The process of operating the ultrasonic probe to electronically scan the material surrounding the pinhole circumferentially to identify cracks present in the material surrounding the pinhole adjacent to the pinhole receiving the probe Is provided.

  Referring now to FIG. 1, a rotor wheel 10 is shown along which a plurality of buckets 12 (only one bucket 12 is shown in the figure) are to be mounted. The rotor wheel 10 includes a dovetail extending in the circumferential direction indicated by reference numeral 13 in the figure, and the dovetail 13 is composed of a plurality of circumferentially extending fingers 14 projecting radially outward. Has a groove 16 defined therein. The fingers extend along the outer edge of the wheel 10. Groove 16 receives a dovetail that is complementary to the groove, indicated by reference numeral 17, composed of a plurality of fingers 18 that form part of bucket dovetail 20. It will be appreciated that the fingers 14 defining the wheel dovetail 13 mesh with the fingers 18 defining the bucket dovetail 17. As shown, the protruding fingers of each wheel and bucket at each circumferential position of the bucket along the wheel have a plurality of alignment holes or pinholes 22 and 24 extending in the axial direction. FIG. 1 shows, for each bucket, three radially aligned holes at each circumferential position of the bucket along the wheel. It will be appreciated that the aligned alignment pinholes 22 and 24 are located along the radius of the wheel and are spaced equidistantly and circumferentially along the circumference of the wheel. Pins 26 are used to secure bucket 12 to wheel 10 and are received through alignment pin holes 22 and 24. In the illustrated embodiment, three pinholes and thus three pins are provided to secure each bucket to the wheel. It is understood that the bucket dovetails are stacked together to form a circumferential array of buckets along the wheel, and in use, bucket 12 is located in the hot fluid flow path of the turbine, eg, the steam flow path of the steam turbine. Will.

  Referring to FIG. 1, it will be appreciated that the radially aligned pins 26 and the fingers 14 of the wheel 10 resist the centrifugal forces acting on the bucket during turbine operation. During use, cracks 30 may develop over time in the material around the wheel fingers 14 and bucket fingers 18, particularly the pinholes that penetrate the wheel 10. The crack usually runs almost in the circumferential direction and spreads in the circumferential direction or the tangential direction, but in many cases, the crack spreads from one pinhole and is connected to an adjacent pinhole. As pointed out above, when the bucket is removed from the wheel 10 by removing the pin 26 and bucket, several test procedures can be utilized to detect those cracks. However, removing all pins and buckets is time consuming and cumbersome and is therefore an expensive operation, and according to the present invention, this operation is avoided.

  In accordance with a preferred embodiment of the present invention, finger dovetails 13 and 17 are removed in situ, i.e. without removing the bucket from the edge of the wheel, by removing a limited number of pins around the wheel. A method for inspection is provided. For example, referring to FIG. 2, the initial process of the preferred method of the present invention is the intermediate pin of three radially aligned pins holding every other bucket along the circumference of the wheel 10. Including removing. The circumferential spacing between pins removed to enable the inspection method of the present invention may include a wider circumferential spacing between every other circumferentially spaced pin. good. For example, an intermediate pin in every second or third group of pins along the peripheral edge may be removed. Thus, an intermediate pin of the three radially aligned pins 26 will be removed at selected circumferential positions along the edge of the wheel. The pins may be removed by hammering the pins out of the aligned pin holes. Alternatively, the pins may be extruded, a gun loaded with explosives may be used to pop one or more pins out of the pinhole, or one or more pins may be removed using an EDM process You may do it.

  When the pins are removed, individual ultrasonic probes or phased array ultrasonic probes 40 (FIG. 5) having one or more piezoelectric elements are respectively aligned with the pinholes where the pins are removed. Insert and inspect the dovetail for cracks in the wheel and bucket dovetail material around the pinhole adjacent to the pinhole receiving the probe. Although the probe 40 is described herein as a phased array ultrasonic probe, the probe may include one or more piezoelectric elements along its surface, in which case it determines ultrasonic information regarding analysis and crack detection. It will be appreciated that to perform a complete circumferential scan with respect to the pinhole axis, it is necessary to mechanically rotate the probe within the aligned pinwheel. In either case, the probe 40 is preferably cylindrical in shape to closely align with the circumferential extent of the aligned pinholes, but it is not essential. One preferred embodiment using a phased array ultrasound probe 40 includes a plurality of generally linear piezoelectric elements 42 (FIG. 5) that are spaced apart from one another along the circumference of the probe 40. As shown in FIG. 5, the longitudinal direction of each piezoelectric element 42 coincides with the axial direction of the probe. The piezoelectric element 42 may be curved along its outer surface or may be flat. In terms of dimensions, the probe has a diameter that allows the probe to be inserted into the aligned pinhole with minimal spacing between the cylindrical surface of the probe and the face of the aligned pinhole to improve resolution. Have The individual piezoelectric elements of the ultrasonic probe with an appropriate time delay between the piezoelectric elements 42 to allow generation of an ultrasonic beam that can be focused and directed to inspect the material surrounding the hole. It will be appreciated that element 42 may be pulsed. That is, the ultrasonic beam can be directed 360 ° around the hole without mechanically rotating the probe about its cylindrical axis. Therefore, the circumferential scanning of the finger dovetail can be realized without displacing the probe other than in the axial direction. Electronically oscillates the ultrasonic beam by displacing the phased array probe axially by mechanical means (not shown) and pulsing the individual piezoelectric elements 42 with appropriate time delays. In combination, the complete scanning of the material around the hole is possible. By synchronizing the axial scan with the ultrasonic pulse motion, a continuous spiral scan pattern can be generated as the probe is continuously displaced axially within the pinhole. Alternatively, it is possible to perform a circumferential scan at one axial distance and then gradually advance the probe in the axial direction to form a scan / index path over the entire inspection range. Either way, the inspection range of the material can be completely covered by only one mechanical degree of freedom of the probe, ie by the axial movement of the probe.

  It will be appreciated that the probe may take different forms other than the two forms previously described. For example, as shown in FIG. 6, another probe 43 has a piezoelectric element 44 that guides ultrasonic energy in the axial direction. The piezoelectric element 44 is axially aligned with a mirror 46 at one end of the probe, the mirror being conical and arranged at an angle with respect to the axis of the probe 43. An axially traveling ultrasound beam is reflected from the mirror and is directed substantially radially into the finger dovetail material. By sequentially pulsing the piezoelectric element 44, the pulsed electron beam is rotated about the probe axis. It will also be appreciated that the ultrasound beam can be focused at different distances from the probe. The position of the probe can be encoded, and when combined with an ultrasound beam that shows the reflected beam from the crack returned to the probe, the inspection data can be accurately imaged for analysis.

  Referring to FIG. 4, in order to check for cracks in the dovetail material adjacent to the pinhole that surrounds the pinhole receiving the probe, an intermediate pinhole of the radially aligned pinholes is How it is used is shown schematically by example. Therefore, as shown in FIG. 4, with the probe 40 inserted in the intermediate pinhole 50, the ultrasonic beam is pulsed in the circumferential direction around the pinhole 50, or with respect to the probe axis in the pinhole. The presence of cracks in the dovetail material surrounding the pinholes that are radially adjacent to the pinhole receiving the probe and circumferentially adjacent to the pinhole by being physically rotated by mechanical rotation. Can be inspected. It will also be understood that cracks extending from the pinhole in which the probe is inserted are difficult to detect. In other words, the resolution of the probe is easier to detect for cracks in the dovetail material starting from the pinhole adjacent to the pinhole receiving the probe. Therefore, when the ultrasonic inspection is completed and the probe is pulled out from the pinhole 50, the pinhole 50 itself can be inspected by another method such as using an eddy current.

  Furthermore, the material surrounding the radially aligned pinholes on both circumferential sides of the pinhole in which the probe is inserted is inspected as shown in FIG. 4, but with a smaller number of probes (thus It will be appreciated that it may be used as part of a sampling technique that uses pinholes (which also reduces the number of pins removed). That is, by removing the pins at wider circumferential distances or intervals along the edge of the wheel, the wheel and bucket dovetail material can be inspected for cracks as part of the statistical sampling. By performing sampling for the presence or absence of crack formation, the probability of crack formation at a particular wheel and bucket combination can be predicted fairly accurately. Therefore, if no cracks are clearly indicated by the sampling technique, the probability that no finger dovetail has cracks is very high. If the sampling technique identifies only one or more cracks, it can be said that the probability of further cracks occurring in the particular wheel / bucket combination undergoing inspection is very low. Thus, it is possible to repair only dovetails in which one or more cracks have been detected with a great deal of confidence that no cracks remain in the wheel / bucket combination. On the other hand, if a significant number of cracks are manifested by sampling, all buckets will need to be removed as needed to inspect and repair the finger dovetail more thoroughly. Will.

  Thus, it will be appreciated that the method of the present invention requires removing only a minimal number of pins around the wheel without removing one or more buckets from the wheel. As such, this inspection method is relatively quick and exhibits high sensitivity for inspection of cracks extending from the dovetail pinholes of the wheel and bucket.

  The invention has been described with reference to what is considered to be the most practical and preferred embodiment at the present time. In addition, the code | symbol described in the claim is for easy understanding, and does not limit the technical scope of an invention to an Example at all.

The partial perspective view which shows a part of circumference | surroundings of the bucket fixed to the turbine wheel and the wheel. FIG. 2 is a view similar to FIG. 1 illustrating the removal of selected pins according to a preferred method of ultrasonic inspection of a wheel / bucket dovetail according to the present invention. The figure similar to FIG.1 and FIG.2 which shows insertion of the ultrasonic probe to the pinhole from which the pin is removed. FIG. 3 is a schematic diagram illustrating scanning of an ultrasonic probe to define the location of a crack present in a finger dovetail near an adjacent pinhole. Schematic which shows a phased array ultrasonic probe. The cross-sectional perspective view which shows schematically the phased array probe of a different form in the aligned pinhole.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Rotor wheel, 12 ... Bucket, 13 ... Wheel dovetail, 14 ... Finger, 17 ... Bucket dovetail, 18 ... Finger, 20 ... Bucket dovetail, 22, 24 ... Pinhole, 26 ... Pin, 30 ... Crack, 40 ... Phased Array ultrasonic probe, 42 ... piezoelectric element, 43 ... probe, 44 ... piezoelectric element, 50 ... pinhole

Claims (14)

Accommodating a turbine wheel (10) and bucket (12) to one another solid Chakusuru plurality of pins, wheels for the presence of cracks in the surrounding material in the circumferential direction and radially aligned plurality of pinholes (22, 24) In the method for in-situ inspection of dovetails and bucket dovetails (13, 17),
Removing the pin (26) from the pinhole without removing the bucket from the wheel;
Inserting an ultrasonic probe (40) into the pinhole from which the pin has been removed ;
The pin was removed so as to electronically scan the material around the pinhole from which the pin was removed to identify cracks present in the material around the pinhole from which the pin was removed inside the pinhole, Ri consists a process of rotating the ultrasonic probe with respect to its axis,
The removing process is an intermediate pinhole (50) of the radially aligned pinholes (22, 24), and at least every other pinhole (50) in the circumferential direction. The method is characterized by removing only the pins of the pinhole (50) . Wheel dovetail for cracking of material around a plurality of circumferentially and radially aligned pinholes (22, 24) containing a plurality of pins that secure the turbine wheel (10) and bucket (12) together And in-situ inspection of bucket dovetails (13, 17),
Removing the pin (26) from the pinhole without removing the bucket from the wheel;
Inserting a phased array ultrasonic probe into the pinhole from which the pin has been removed ;
The pin from which the pin has been removed so as to electronically scan the material around the pinhole from which the pin has been removed to identify cracks present in the material around the pinhole from which the pin has been removed Ri consists a step of operating the ultrasonic probe within the hole,
The removing process is an intermediate pinhole (50) of the radially aligned pinholes (22, 24), and at least every other pinhole (50) in the circumferential direction. The method is characterized by removing only the pins of the pinhole (50) . Process of the operation, the ultrasonic beam around the pin hole the pin without mechanically rotating relative to the pin hole the pin ultrasound probe has been removed (50) has been removed (50) The method of claim 2 including directing in a circumferential direction. The method of claim 2, comprising providing a cylindrical probe having a plurality of substantially linear linear elements (42) along a cylindrical surface of the probe. Providing a cylindrical probe having a plurality of piezoelectric elements arranged to direct ultrasonic energy in an axial direction and reflecting the axially induced energy in a substantially radial direction. The method described. Electronically rotating the ultrasound beam simultaneously with inserting the ultrasound probe axially into the pinhole from which the pin has been removed to generate a continuous spiral scanning path. Item 3. The method according to Item 2. At each axial pinhole (50) position, the pin is positioned at a plurality of axially spaced positions along the length of the pinhole (50) from which the pin has been removed. In order to scan the material around the removed pinhole (50) in the circumferential direction, the ultrasonic probe is gradually advanced axially into the pinhole (50) from which the pin has been removed. The method of claim 2 including electronically rotating the beam. The method according to claim 1 or 2, characterized in that the intermediate pinhole (50) is an intermediate pinhole out of three radially aligned pinholes (22, 24). The method of claim 1 including providing a cylindrical probe having a plurality of substantially elongated linear piezoelectric elements along a cylindrical surface of the cylindrical probe. Scan the material circumferentially with respect to the pinhole at each incremental axial location to form a circumferential scan path at a plurality of axially spaced locations along the pinhole (50) from which the pin has been removed. The method of claim 1 , comprising gradually advancing the ultrasound probe axially into the pinhole (50) from which the pins have been removed and electronically rotating the ultrasound beam. The method of claim 1 , comprising reinserting the pin into the pinhole (50) from which the pin has been removed . The method of claim 11 , comprising inspecting the pinhole for cracks before reinserting the pin into the pinhole. A piezoelectric element (44) for guiding the ultrasonic energy in the axial direction, and a mirror (axially aligned with the piezoelectric element at one end of the ultrasonic probe to reflect the ultrasonic beam and guide it in the radial direction ( 46. The method according to claim 1, wherein an ultrasonic probe is used.  3. The method according to claim 1, further comprising a step of pulling out the ultrasonic probe from the pinhole (50) and inspecting the pinhole itself by a method different from an inspection method using the ultrasonic probe. the method of.